During production, many products are subjected to heat treatment for various reasons, including thermal curing during semiconductor wafer fabrication, annealing operations to harden a material of the product, such as steel, or the like. Often times, the heat treatment process is carried out at very high temperatures. Dryers comprising conveyors for drying components placed thereon are widely used in a variety of industries.
One such application includes dryers for fusing or drying a conductive metallization paste onto silicon wafers for photovoltaic cells. Such dryers typically transport the silicon wafers on a conveyor through an enclosure wherein infra-red (IR) heaters and very small amount of process air, if any, is introduced and/or removed from the dryer enclosure. In some such dryers, some process air is introduced into the enclosure through the surrounding insulation or via sparge tubes. As volatile organic compounds (VOCs) are evaporated from the paste, a mixture of the fluid including air and the vaporized compounds from within the enclosure is extracted through exhaust ports at the entrance and/or exit of the enclosure. As such, the process air does not contribute to the drying process, but merely functions as an agent or a means for removing the vaporized compounds from within the enclosure.
Some dryers do not use IR heaters, but employ re-circulated forced air. However, the air is generally introduced into the enclosure at low velocities and is therefore not efficient at removing the vaporized compounds. Because re-circulated air is used, the concentration of the vaporized compounds eventually reaches a saturation point at which extraction of the vaporized compounds may not be possible. Furthermore, the vaporized compounds start condensing within the ductwork and other components of the system, requiring frequent shut-downs for maintenance.